全文获取类型
收费全文 | 2135篇 |
免费 | 47篇 |
国内免费 | 9篇 |
专业分类
化学 | 1517篇 |
晶体学 | 27篇 |
力学 | 35篇 |
数学 | 98篇 |
物理学 | 514篇 |
出版年
2023年 | 9篇 |
2021年 | 15篇 |
2020年 | 17篇 |
2019年 | 28篇 |
2018年 | 23篇 |
2016年 | 25篇 |
2015年 | 32篇 |
2014年 | 59篇 |
2013年 | 78篇 |
2012年 | 110篇 |
2011年 | 117篇 |
2010年 | 60篇 |
2009年 | 78篇 |
2008年 | 106篇 |
2007年 | 134篇 |
2006年 | 124篇 |
2005年 | 122篇 |
2004年 | 85篇 |
2003年 | 90篇 |
2002年 | 85篇 |
2001年 | 63篇 |
2000年 | 33篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 31篇 |
1992年 | 36篇 |
1991年 | 28篇 |
1990年 | 37篇 |
1989年 | 24篇 |
1988年 | 33篇 |
1987年 | 36篇 |
1986年 | 34篇 |
1985年 | 38篇 |
1984年 | 33篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 28篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 9篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有2191条查询结果,搜索用时 15 毫秒
1.
Dr. Nozomi Mihara Dr. Yasuyuki Yamada Dr. Hikaru Takaya Prof. Yasutaka Kitagawa Dr. Kazunobu Igawa Prof. Katsuhiko Tomooka Prof. Hiroshi Fujii Prof. Kentaro Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3369-3375
Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 5+, which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 5+ catalyzed ethane oxidation in the presence of H2O2 at a relatively low temperature. The site-selective complexation of 3 5+ with an additional anionic porphyrin (TPPS4−) through π–π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 5+ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS4− to 3 5+ enhanced the catalytic activity. 相似文献
2.
Jun Fujii Giancarlo Panaccione Giorgio Rossi Giancarlo Trimarchi 《Surface science》2006,600(18):3884-3887
Bulk carbon impurities segregate at the Fe(1 0 0) surface and, upon thermal annealing, can form metastable surface phases with local and long range order and peculiar electronic properties. We present a surface science study of C-segregated Fe(1 0 0) with scanning tunneling microscopy, angle resolved photoemission, and ab initio calculations of the surface structure and electron states. In particular the c(3√2 × √2) structure, observed for 0.67 atomic layers of C segregated at the iron surface, is found to be due to self-organized carbon stripes made of zig-zag chains. The strong hybridization between C and Fe was observed in ARPES spectra. 相似文献
3.
To find an effective extraction and removal method for palladium(II), which is one of the main fission products from an acidic nuclear spent fuel solution, the extraction behavior of palladium(II) from a nitric acid medium by an acidic chelating extractant, 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5-one (HPMTP) and a tertiary amine of high molecular weight, tri-n-octylamine (TOA), has been studied by spectrophotometry. A noticeable antagonistic extraction effect was observed in the extraction system under the given conditions. To understand this phenomenon, a preliminary investigation was performed to explain the mechanism of this reaction. According to the theory of corresponding solutions (TCS), the association reaction between HPMTP and TOA is proposed in the organic phase. An associated species, HPMTP·TOA, formed through hydrogen bonding in a chloroform medium might be the main reason why an antagonistic extraction effect occurred. The association constant between HPMTP and TOA was calculated to be 2.86±0.05. 相似文献
4.
The propagation characteristics of shear horizontally polarized (SH) waves passing through (Ni42Nb28Zr30)100–x Hx (x = 0–15.2) glassy alloys were investigated as a function of hydrogen content. With an increase in hydrogen content, the propagation time and main frequency of the receiving waves show increase and decrease, respectively, indicating expan‐ sion in average atomic distance which comes from solution of hydrogen. In sharp contrast to crystalline alloys, the decrease in damping ratio and the delay in phase with increasing hydrogen suggest a strong settlement of hydrogen into four‐coordination sites surrounded tetrahedrally by four Zr atoms and the resulting increase in dynamic elasticity, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
The potential of the internal rotation of the methyl group was determined for o-, m-, and p-fluorotoluene cations by pulsed field ionization spectroscopy. The potential of the internal rotational motion was also surveyed for other toluene derivative cations. It was found that the barrier height generally increases by ionization. The increase in the barrier height has been discussed in connection with the reduction of the internal rotational constant B by ionization. The geometrical distortion of the methyl group during the internal rotation has been suggested. 相似文献
6.
7.
8.
9.
10.